This invention concerns diagnostic procedures and techniques for amplifying a nucleic acid sequence. The detection and quantitation of a specific nucleic acid sequence (i.e., a target sequence) is an increasingly important technique having numerous applications including identifying and classifying microorganisms, diagnosing infectious diseases, detecting and characterizing genetic abnormalities, identifying genetic changes associated with cancer, studying genetic susceptibility to disease, measuring the response to various types of treatment, identifying criminal suspects, and resolving paternity disputes.
A common method for detecting and quantitating target nucleic acid sequences is nucleic acid hybridization. Nucleic acid hybridization, typically, uses a labeled nucleic acid probe having a nucleic acid sequence complementary to the target sequence. The probe is mixed with a sample suspected of containing the target sequence under conditions suitable for hybrid formation. The probe then hybridizes to the target sequence present in the sample. Hybridization can be detected by various techniques well known in the art. These techniques include selectively degrading the label present on unhybridized probe and then measuring the amount of label associated with the remaining hybridized probe (Arnold et al., PCT US88/02746).
Numerous methods are available for amplifying nucleic acid strands (i.e., nucleic acid polymers) to increase the amount of target sequence. These methods use the nucleic acid strand containing the target sequence as a template to produce a complementary nucleic acid strand containing the target sequence. Such methods include the polymerase chain reaction method (PCR), as described by Mullis et al., (See U.S. Pat. Nos. 4,683,195, 4,683,202, and 4,800,159 and European Patent Application Nos. 863022-98.4, 86302299.2, and 87300203.4, and Methods in Enzymology, Volume 155, 1987, pp. 335-350). PCR involves the use of a pair of specific oligonucleotides as primers for the two complementary strands of the double-stranded DNA containing the target sequence. The primers are chosen to hybridize at the ends of each of the complementary target strands, 3′ of the target sequence. Template-dependent DNA synthesis, on each strand, can then be catalyzed using a thermostable DNA polymerase in the presence of the appropriate reagents. A thermal cycling process is required to form specific hybrids prior to synthesis and then denature the double stranded nucleic acid formed by synthesis. Repeating the cycling process geometrically amplifies the target sequence. A PCR method may also be used with an RNA target using RNA-dependent DNA polymerase to create a DNA template.
The PCR method has been coupled to RNA transcription by incorporating a promoter sequence into one of the primers used in the PCR reaction and then, after amplification by the PCR method, using the double-stranded DNA as a template for the transcription of single-stranded RNA. (See, e.g., Murakawa et al., DNA 7:287-295 (1988)). Other amplification methods use multiple cycles of RNA-directed DNA synthesis and transcription to amplify DNA or RNA targets (See, e.g., Burg et al., WO 89/1050; Gingeras et al., WO 88/10315 (sometimes called transcription amplification system or TAS); Kacian and Fultz, EPO Application No. 89313154; Davey and Malek, EPO Application No. 88113948.9; Malek et al., WO91/02818). Urdea, WO91/10746, describe a method that achieves signal amplification using a T7 promoter sequence.
The ligase chain reaction (LCR) is described in European Patent Publication 320,308. This method requires at least four separate oligonucleotides, two of which hybridize to the same nucleic acid template so their respective 3′ and 5′ ends are juxtaposed for ligation. The hybridized oligonucleotides are then ligated forming a complementary strand on the nucleic acid template. The double-stranded nucleic acid is then denatured, and the third and fourth oligonucleotides are hybridized with the first and second oligonucleotides that were joined together. The third and fourth oligonucleotides are then ligated together. Amplification is achieved by further cycles of hybridization, ligation, and denaturation. The Qβ replicase (QβR) method described in PCT Publication No. 87-06270 and U.S. Pat. No. 4,786,600 uses a specific RNA probe which is capable of specific transcription by a replicase enzyme. The method requires the design and synthesis of RNA probes with replicase initiation sites.
Amplification methods using palindromic probes are described in EPO Publication Nos. 0427073A and 0427074A. The palindromic probe forms a hairpin with a nucleic acid target sequence. The probe contains a functional promoter located in the hairpin region from which RNA transcripts are produced.
Walker et al., Proc. Natl. Acad. Sci. U.S.A., 89:392-396 (January 1992), Walker et al., Nucl. Acids Res. 20: 1691-1696 (1992), European Patent Application No. EP 0 497 272 A1, and European Patent Application No. EP 0 500 224 A2, describe an oligonucleotide-driven amplification method using a restriction endonuclease. The restriction endonuclease nicks the DNAIDNA complex to enable an extension reaction and, therefore, amplification. Becker, et al., EPO Application No. 88306717.5, describe an amplification method in which a primer is hybridized to a nucleic acid sequence and the resulting duplex cleaved prior to the extension reaction and amplification.
Noonan, K. E. et al., Nucl. Acids Res. 16, 10366 (1988), describe using random hexamers to prime reverse transcriptase in a random, nonspecific manner for the synthesis of cDNA from mRNA. Amplification of the desired target is accomplished with PCR.
Feinberg, A. P. et al., Anal. Biochem. 132, 6 (1983), and Liang, W. et al., Nucl. Acids Res. 16,3579 (1988), describe the synthesis of DNA strands complementary to a DNA template by combining single-stranded DNA with random hexanucleotide primers, deoxynucleoside triphosphates, buffer, the Klenow fragment of E. coli DNA polymerase I, and a labeled deoxynucleoside triphosphate.
A related process, known as Random Priming Amplification (RPA) for amplifying nucleic acid is described by Hartley, U.S. Pat. No. 5,043,272. According to Hartley, at columns 2-3, lines 63-2:                The process includes the steps of priming single-stranded template nucleic acid strands with an excess of random oligonucleotide primers and incubating the single-stranded template nucleic acid strands and excess random oligonucleotide primers in the presence of excess amounts of an inducing agent, a strand displacement agent, and nucleoside triphosphate substrates to randomly amplify nucleic acid strands.        